1. Field of the Invention
This invention relates to a constant current circuit and, more particularly to a constant current circuit for a semiconductor integrated circuit which can supply a relatively large current without enlargement of the chip size.
2. Description of the Prior Art
In semiconductor integrated circuits, diodes and transistors formed on the same pellet can be made with matching characteristics and therefore a constant current circuit in which the current is equal to or amounts to several times the bias current can easily be made. Now, in the known costant current circuit wherein a diode D for a bias stage is connected to the emitter of an output transistor Q, the emitter regions of the diode D and transistor Q are formed so that the ratio of those emitter areas is 1:N, for instance. In this case, the relationship of the constant current output I.sub.2 flowing through the collector of the transistor Q to the bias current I.sub.1 flowing through the diode D becomes I.sub.2 /I.sub.1 = N, and in the case for which the value of N is close to 1 it is possible to obtain a constant current circuit with an extremely simple structure. If, however, the current consumption in the integrated circuit as a whole must be made small, for instance if a constant current output of 10 mA is to be obtained, then in order to make the bias current 1 mA, the emitter area of the transistor Q must be given a value which is 10 times that of the emitter area of the diode D, and therefore the chip size becomes large and this is therefore disadvantageous.
Also, if the aforesaid area ratio is made less than 10, for example, then the bias current is increased, and the current cnsumption in the integrated circuit as a whole increases and therefore this too is disadvantageous.